Conversion of power is performed usually in switched mode consisting of turn-on and turn-off statuses.
In semiconductor power stages the energy dissipation is essentially determined by conducting and switching losses. With increasing frequency the switching losses become dominant, since the switching process is executed much more frequently. This circumstance limits the economically achievable maximum switching frequency, which is determined by dedicating one third to one half of the total losses to switching losses. This leads to approx. 10 kHz switching frequency with state-of-the-art IGBTs of the 600V class and 4 kHz for state-of-the-art 1200V devices.
Each operation of turn-on and turn-off is completed in a limited period of time and the duration for the turn-on and turn-off status of the switching components is determined by the properties of the parts forming said converter. Each turn-on or turn-off operation will cause power consumption. The value of the switching consumption equals to the value obtained by integrating multiplication of the current flowing in the switching components by the voltage across the switching components over the duration of one turn-on or turn-off operation. Thus, the higher the switching frequency of the switching component is, the more the switching consumption becomes. Especially when the frequency is very high, such switching consumption becomes majority of the consumption and can increase the aggregate switching consumption of the switching components. Such switching consumption will cause negative influences to the switching components, increase the working temperature, the excursion of working parameters of the switching components, and will finally also waste electrical energy—which should be saved in battery operated vehicles and devices, etc.
In order to diminish this kind of switching consumption, many technologies relating to soft-switching are being developed. The working principle of these technologies is to make the current flowing through or the voltage across the switching components be zero or near zero during the turn-on and turn-off operation. In this way, the switching consumption shall be decreased accordingly. These types of soft-switching technology can only be used in DC power converters, and auxiliary circuits of such types of soft-switching are mostly of great complexity with multiple components, examples for such solutions are disclosed in e.g. U.S. Pat. No. 5,066,900; U.S. Pat. No. 6,016,258 and EP1458084.